Flame retardant (FR) fabrics are crucial in both military and non-military environments. Firefighters, race car drivers, and petro-chemical workers are just a few of the non-military groups that benefit from the added protection of flame retardant fabrics. However, the true benefit of flame retardant fabrics lies with the military. In addition to the unforgiving surroundings that our military troops must operate in, the advent of unconventional modern warfare creates an even more hostile environment. Specifically, the use of improvised explosive devices (“IEDs”) to immobilize large convoys of soldiers makes individual troop protection critically important.
In addition to ballistic fabrics and body armor, flame retardant fabrics serve a crucial role in protecting soldiers from IEDs. IEDs are constructed of numerous materials (e.g. high-explosive charges, flammable liquids, shrapnel, etc.), some acting as projectiles and others acting as incendiaries upon detonation. Thus, military fabrics must be of varied construction to handle the multitude of threats from an IED.
There are basically two types of flame retardant fabrics used in protective clothing: (1) Fabrics made from flame retardant organic fibers (e.g. aramid, flame retardant rayon, polybenzimidazole, modacrylic, etc.); and (2) Flame retardant fabrics made from conventional materials (e.g. cotton) that have been post treated to impart flame-retardancy. Nomex® and Kevlar® aromatic polyamides are among the most common types of flame retardant synthetic fibers. These are made by solution spinning a meta- or para-aromatic polyamide polymer into fiber. Aromatic polyamides do not melt under extreme heat, are naturally flame retardant, but must be solution spun. Unfortunately, Nomex® is not very comfortable and it is difficult and expensive to produce. Kevlar® is also difficult and expensive to produce.
Post-treatment flame retardants are applied to fabrics and can be broken down into two basic categories: (1) Durable flame retardants; and (2) Non-durable flame retardants. For protective clothing, the treatment must withstand laundering, so only durable treatments are selected. Today, most often, durable flame retardant chemistry relies on phosphorus-based FR agents and chemicals or resins to fix the FR agents on the fabric.
One polymer fiber that has been widely studied because of its processability and strength is nylon 6,6 fiber. A small amount—about 12%—of aliphatic nylon fibers can be blended with cotton and chemically treated to produce a flame retardant fabric. Because cotton is the major fiber component, this fabric is called “FR cotton” fabric. Nylon fibers impart superior wear resistance to FR cotton fabrics and garments. However, because nylon is melt processable (i.e. thermoplastic) and offers no inherent flame resistance, the quantity of nylon fiber in an FR fabric is limited. Attempts to chemically modify aliphatic nylon fibers and increase nylon fiber content, while still achieving adequate flame retardancy, have been unsuccessful. In fact, Deopura and Alagirusamy state in their recent book Polyesters and Polyamides (The Textile Institute 2008 at page 320) that “[i]t seems unlikely that there will be any major breakthroughs with regard to new and/or improved reactive flame-retardant comonomers or conventional . . . flame retardant additives for use in . . . nylon fibers.”